Signal Generating System For Internal Combustion Engines

Abstract

A signal generating system for use in internal combustion engines comprising a rotary pole means secured to a shaft rotating in synchronism with the engine crankshaft, said rotary pole means having a plurality of pole tips, a stationary pole means having a plurality of pole tips, a permanent magnet magnetically coupling the rotary and stationary pole means, and an induction coil to convert the rate of change of magnetic flux, which is provided by the permanent magnet, into a corresponding voltage. Two signals of different voltage levels are derived from the induction coil, and from these signals the top dead center, etc., of a particular cylinder and the successive predetermined angular position of the engine crankshaft may be detected.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to signal generating systems for use in internal combustion engines and, more particularly, to signal generating systems for providing signals to control the fuel injection system or ignition system of internal combustion engines.

2. Description of the Prior Art

In the usual signal generating system for internal combustion engines, a generator with the rotor rotating in synchronism with the engine crankshaft has been used. However, signal pulses produced by such generator have the same waveform so that it has been extremely difficult to distinguish the individual output pulses. Therefore, it has been difficult to employ this system for an ignition system where low-voltage ignition signal is successively distributed to a plurality of ignition coils without any high-voltage distributor. Also, in a fuel injection system of an internal combustion engine, in which the air-fuel mixture is injected into the individual cylinders during the respective fuel injection periods, it is necessary to detect the top dead center, etc., of at least one cylinder. This function cannot be provided by the usual signal generator using the afore-said generator.

SUMMARY OF THE INVENTION

An object of the invention is to provide a signal generating system for use in internal combustion engines comprising a rotary pole means secured to a shaft rotating in synchronism with the engine crankshaft, said rotary pole means having a plurality of pole tips, a stationary pole means having a plurality of pole tips, a permanent magnet magnetically coupling the rotary and stationary pole means, and an induction coil to convert the rate of change of magnetic flux provided by the permanent magnet into a corresponding voltage.

Another object of the invention is to provide a signal generating system for use in internal combustion engines, in which the rotary and stationary pole means are coupled to each other such that when a particular one of the pole tips of the rotary pole means passes by a particular one of the pole tips of the stationary pole means a greater rate of change of magnetic flux linking with the induction coil results to induce a greater voltage surge across the induction coil than when said particular pole tip of said rotary pole means passes by the other pole tips of the stationary pole means, and which further comprises a first detector to provide a detection signal when a detected output produced as a result of integration of the voltage output of the induction coil is at a first level corresponding to the afore-said greater voltage surge, and a second detector to provide a detection signal when the voltage output of the induction coil reaches a second level other than said first level.

One feature of the invention resides in that two different signals can be obtained with a system of a comparatively simple construction having only a single generator. Conventionally, two generators are required to accomplish the same end. More particularly, a first signal indicating a particular angular position of the engine crankshaft, i.e. the top dead center, etc., of a particular cylinder is obtained from the first detector, and a second signal indicating successive predetermined angular positions of the engine crankshaft is obtained from the second detector. Thus, the signal generating system according to the invention is very advantageous when applied to the fuel injection system and ignition system of internal combustion engines.

A further object of the invention is to provide a signal generating system for use in internal combustion engines, in which the rotary and stationary pole means are each provided with a plurality of pole tips respectively located at all but at least one positions corresponding in number to the number of pulses required to be produced for every rotation of the rotor shaft and equally dividing the periphery of each of the rotary and stationary pole means.

With this system the afore-mentioned benefits that two signals at different levels, the one at a higher voltage level indicating a particular angular position of the engine crankshaft, i.e. the top dead center, etc., of a particular cylinder and the other at a lower voltage level indicating successive predetermined angular positions of the engine crankshaft, are obtained and that it can be very advantageously used as the signal source of the fuel injection system and ignition system are also provided. In addition, with this system the rotary and stationary pole means may have a reduced number of pole tips from the number of pulses to be produced by every rotation of the rotor shaft. Also, the complicated steps in the production of both the rotary and stationary pole means can be eliminted. Further, the generator as a unit comprising as component parts the rotary pole means, the stationary pole means, the permanent magnet and the induction coil may be simplified in construction and reduced in size to thereby reduce the manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b show, respectively in section and in plan view, a generator part of a signal generating system for use in internal combustion engines embodying the invention.

FIG. 2 is a schematic diagram showing the electric circuit of the entire system.

FIGS. 3a, 3b and 3c show voltage waveforms appearing at various parts of the same system.

FIG. 4 is a block diagram showing a typical application of the system according to the invention to the fuel injection system of an internal combustion engine.

FIG. 5 is a view similar to FIG. 1a, showing another embodiment of the signal generating system for internal combustion engines according to the invention.

FIGS. 6 and 7 are respectively top and bottom views of the embodiment of FIG. 5.

FIG. 8 is a block diagram showing a circuitry for obtaining two different kinds of signals from the generator according to the invention.

FIGS. 9a, 9b and 9c show voltage waveforms involved in the operation of the arrangement of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawing, and particularly to FIGS. 1a and 1b, there is shown a generator embodying the invention. Numeral 1 generally designates a distributor mounted in an internal combustion engine (not shown). It has a housing 1a and a shaft 1b rotating in synchronism with the engine crankshaft. Numerals 2 and 3 designate respective rotary pole members secured to the distributor shaft 1b by a sleeve member 4a made of a non-magnetic material. The pole member 2 has four peripheral lobes 2a, 2b, 2c and 2d, while the pole member 3 has none. One of the four lobes of the pole member 2, namely lobe 2a, is different from the rest of the lobes in that it perpendicularly projects from the plane of the pole member 2 while the other lobes 2b, 2c and 2d are smaller than the lobe 2a and extend in the plane of the pole member 2. Sandwitched between the upper and lower pole members 2 and 3 is a permanent magnet 4, which is axially polarized with S pole at the top and N pole at the bottom, as shown in FIG. 1. The permanent magnet 4 is also secured to the distributor shaft 1b by the sleeve member 4a. Numeral 5 designates a fixed or stationary magnetic pole member secured to the inside wall surface of the distributor housing 1a which is made of a non-magnetic material. Like the pole member 2, the stationary pole member 5 has four lobes 5a, 5b, 5c and 5d, one of which, namely lobe 5a, upwardly projects so that it can come to face the projected or raised lobe 2a of the rotary pole member 2, while the other lobes 5b, 5c and 5d are smaller than the lobe 5a and are not raised so that they can come to face the lobes 2b, 2c and 2d of the rotary pole member 2 in the same level. Numeral 6 designates an induction coil accommodated in the annular recess 5e of the stationary pole member 5.

In the operation of the construction described above, with the rotation of the distributor shaft 1b in synchronism with the engine crankshaft successive voltage surges are produced in the induction coil 6. When the distributor shaft 1b assumes an instantaneous position as shown in FIGS. 1a and 1b, the lobes 2a, 2b, 2c and 2d of the rotary pole member 2 just face the corresponding lobes 5a, 5b, 5c and 5d of the stationary pole member 5, so that a substantial part of the magnetic flux of the permanent magnet 4 come to pass across the four pairs of facing lobes. Thus, at this instant an extremely large amount of magnetic flux links with the induction coil 6.

After the distributor shaft 1b has rotated 90.degree. from its position of FIGS. 1a and 1b, the lobes find their next respective counterparts. At this instant, the lobes 2a, 2b, 2c and 2d of the rotary pole member 2 are respectively paired with the lobes 5b, 5c, 5d and 5a of the stationary pole member 5. However, since the lobe 2a of the rotary pole member 2 and the lobe 5a of the stationary pole member 5 are arranged such that they will face with each other at a higher level than the level of the remaining lobes as shown in FIG. 1a, the raised lobe 2a and the lobe 5b do not closely face together, nor do the lobe 2d and the raised lobe 5a. Thus, at this instant the amount of magnetic flux linking with the induction coil 6 is less than that in the previous situation.

After the distributor shaft 1b has rotated a further 90.degree., pairs of the lobes 2a and 5c, 2b and 5d, 2c and 5a, and 2d and 5b result. At this instant, the magnetic flux passing between the raised lobe 2a and the lobe 5c and between the lobe 2c and the raised lobe 5a is extremely small, so that the amount of magnetic flux linking with the induction coil 6 is also less and the induced voltage surge is comparatively low.

After a still further rotation of the distributor shaft 1b by 90.degree., pairs of the lobes 2a and 5d, 2b and 5a, 2c and 5b, and 2d and 5c result. At this instant, the magnetic flux passing between the raised lobe 2a and the lobe 5d and between the lobe 2d and the raised lobe 5a is extremely small, so that the amount of magnetic flux linking with the induction coil 6 is also less and the induced voltage is low.

After yet further 90.degree. rotation of the distributor shaft 1b, the situation of FIGS. 1a and 1b results again. In this manner, the pulsating voltage induced in the induction coil 6 may have a waveform as shown in FIG. 3a. In the Figure, the abscissa represents the angular position .theta. of the engine crankshaft, and the ordinate is taken for the generated voltage e from the induction coil 6. The first large swing a.sub.1 takes place about that instant, at which the lobes 2a, 2b, 2c and 2d of the rotary pole member 2 pass by the corresponding lobes 5a, 5b, 5c and 5d of the stationary pole member 5, that is, the instant at which the raised lobes 2a and 5a face each other. The subsequent three small voltage swings a.sub.2, a.sub.3 and a.sub.4 take place respectively around the instant at which the lobes 2a, 2b, 2c and 2d get radially aligned with the respective lobes 5b, 5c, 5d and 5a, around the instant at which the lobes 2a, 2b, 2c and 2d get aligned with the respective lobes 5c, 5d, 5b and 5a and around the instant at which the lobes 2a, 2b, 2c and 2d get aligned with the respective lobes 5d, 5a, 5b and 5c.

It is to be noted that the angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 on the abscissa axis of FIG. 3a are uniformly spaced 90.degree. apart. At the instant of the situation of FIG. 1, the magnetic flux linking with the induction coil 6 is maximum and is about to decrease. Accordingly, by discriminating the angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 a particular position of the engine crankshaft may be correctly detected. In the case of, for instance, a four-cylinder four-cycle engine in which the distributor shaft 1b synchronized to the engine crankshaft is adapted to rotate at one-half the engine crankshaft speed, it is possible to time these angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 to the respective commencements of fuel injection periods. Also, the magnetic flux linking with the induction coil 6 around the instant of the angular position .theta..sub.1 at which the raised lobes 2a and 5a of the respective pole members 2 and 5 are aligned to each other, is large compared to the other situations and is constant irrespective of the engine speed, so that the integration of the voltage surge a.sub.1 by a suitable integrating circuit enables discriminating the angular position .theta..sub.1 independently of the engine speed.

Stated mathematically, the induced voltage e is given as

e = k(d.phi./dt),

where k is proportionality constant, and .phi. is the magnetic flux linking with the induction coil 6. Integration of this equation yields

Apparently, the integral is independent of the engine speed.

Thus, by detecting the angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 and determining the particular angular position .theta..sub.1 from the above integration it is possible to identify, for instance, the commencements of fuel injection periods for individual cylinders and for a particular cylinder.

A circuit for accomplishing the above function is shown in FIG. 2. In figure, numerals 7 and 8 generally designate respective detectors. Numeral 6 designates the induction coil, and numeral 9 the rotor including the pole members 2 and 3 and permanent magnet 4 as shown in FIGS. 1a and 1b. The detector 7 comprises an input resistor 13, and amplifying transistor 14, a load resistor 15 thereof, a coupling resistor 16, bias resistors 17 and 18, a Schmitt circuit of first-stage and second-stage transistors 19 and 22, load resistors 20 and 24, a coupling resistor 21, a resistor 23 serving to determine the Schmitt level, an emitter load resistor 25 common to the transistors 19 and 22, a differentiating circuit of capacitor 26 and resistor 27, a differentiated pulse amplifier transistor 28 and a load resistor 29 thereof. The detector 7 is adapted to provide a pulse train as shown in FIG. 3b. The detector 8 comprises an integrating circuit of resistor 30 and capacitor 31, an input resistor 32, bias resistors 33 and 34, and amplifying transistor 35, a load resistor 36 thereof, a coupling resistor 36a, bias resistors 37 and 38, a Schmitt circuit of first-stage and second-stage transistors 39 and 44, load resistors 40 and 45, a coupling resistor 41, a resistor 42 serving to determine the Schmitt level, an emitter resistor 43 common to the transistors 39 and 44, a differentiating circuit of capacitor 46 and resistor 47, an amplifying transistor 48 and a load resistor 49 thereof. The detector 8 is adapted to provide a pulse train as shown in FIG. 3c. Numeral 50 designates an output terminal at which the pulses of FIG. 3b appear, and numeral 51 another output terminal at which the pulses of FIG. 3c appear.

In the operation of the circuit of FIG. 2, with the rotation of the distributor shaft 1b in synchronism to the engine crankshaft, the rotary assembly 9 rotates to cause the recurrent voltage of the waveform of FIG. 3a to be induced across the induction coil 6. The voltage thus induced is fed through the input resistor 13 and amplified by the transistor 14. With an extremely great degree of amplification degree of the transistor 14, a substantially square-wave voltage appears across the load resistor 15. One of the alternate levels of this square-wave voltage substantially corresponds to the zero level of the induced voltage, so that either ones of the alternate inverting points correspond to the respective angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4. This wave is rendered into a completely square waveform through the Schmitt circuit of transistors 19 and 22. Thus, a square-wave voltage switching at an extremely fast rate appears at the collector of the second-stage transistor 22 of the Schmitt circuit. The inverting points of this square wave corresponding to the angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 are detected by the differentiating circuit of capacitor 26 and resistor 27, and the detected output is amplified by the transistor 28 to produce output pulses as shown in FIG. 3b at the output terminal 50.

The induced voltage is also supplied to the integrating circuit of resistor 30 and capacitor 31. As a result, across the capacitor 31 there are developed large voltage surges around the angular position .theta..sub.1 independently of the engine speed and small voltage surges around the respective angular positions .theta..sub.2, .theta..sub.3 and .theta..sub.4. The output of the integrating circuit is then amplified by the transistor 35, which is biased through the resistors 33 and 34. Thus, an output signal as a result of amplification of only the large voltage surges around the angular position .theta..sub.1 appears across the load resistor 36. The output signal thus produced is shaped by the Schmitt circuit of transistors 39 and 44 to produce a square-wave voltage switching only in the vicinity of the angular position .theta..sub.1. The resultant output is then differentiated by the differentiating circuit of capacitor 46 and resistor 47, followed by the amplification through the transistor 48 to provide signal pulses in the vicinity of the angular position .theta..sub.1 as shown in FIG. 3c at the output terminal 51.

As has been described, with a single signal generator of the construction shown in FIGS. 1a and 1b two different signals, namely a train of pulses occurring around the successive angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 as shown in FIG. 3b and the other train of pulses occurring only around the angular position .theta..sub.1 as shown in FIG. 3c, can be obtained.

FIG. 4 shows, in block form, a typical application of the signal generator according to the invention to the fuel injection system of an internal combustion engine. In the Figure, reference numeral 100 designates the signal generator shown in FIGS. 1a and 1b, numeral 7 the afore-described detector to provide signal pulses in the vicinity of the angular positions .theta..sub.1, .theta..sub.2, .theta..sub.3 and .theta..sub.4 as shown in FIG. 3b, and numeral 8 designates the afore-said detector to provide signal pulses in the vicinity of only the angular position .theta..sub.1 as shown in FIG. 3c. Numeral 130 designates a fuel control means which represents the quantity of fuel corresponding to various engine-operating parameters. The output signal of the fuel regulator 130 is fed together with the output signal (hereinafter referred to as injection commencement signal) of the detector 7 to a fuel injection signal generator 140. The output signal of the fuel injection signal generator 140 is fed together with the output signal (hereinafter referred to as injection commencement signal) concerning the angular position .theta..sub.1 for a particular cylinder produced by the detector 8 to a fuel injection signal distributor 150, which is connected to a plurality of electromagnetic fuel injection valves 151, 152, 153 and 154 for the respective cylinders.

In the operation of the system just described, as soon as the fuel injection signal distributor 150 receives the injection commencement signal from the detector 8, it gives a command to commence fuel injection to the fuel injection valve of a particular cylinder (for instance the first cylinder). At this time, the fuel injection period is determined by the fuel injection signal of the fuel injection signal generator 140; during this period the electromagnetic fuel injection valve 151 for the particular cylinder is energized from the fuel injection signal distributor 150. Upon appearance of the next fuel injection signal at the fuel injection signal distributor 150, it commands fuel injection with respect to the next cylinder (for instance, the second cylinder); at this time, the electromagnetic fuel injection valve 152 is energized in accordance with the fuel injection signal. Similarly, the electromagnetic fuel injection valves 153 and 154 are successively energized under the command of the fuel injection signal distributor 150. Then, a fuel injection command with respect to the particular cylinder is given again. In the above manner, the sequence is repeated.

The signal generator according to the invention may also be utilized in the ignition system where low-voltage ignition signal is successively distributed to a plurality of ignition coils in a manner analogous to the afore-described mode of operation.

FIGS. 5 to 7 show a second embodiment of the invention. In the Figures, numeral 101 generally designates a distributor mounded in an internal combustion engine (not shown). It has a housing 101a and a shaft 101b rotating in synchronism with the engine crankshaft. Numerals 102 and 103 respectively designate disk-like rotary pole members made of a magnetic material and secured to the distributor shaft 101b by a sleeve member 104 made of a non-magnetic material. They are provided respectively with lobes 102a, 102b and 102c and with lobes 103a, 103b and 103c. In this embodiment, the lobes in each rotary pole member are located at three of the four positions (corresponding in number to the number of cylinders) equally dividing the periphery of the member. The lobes 102a, 102b and 102c axially overlap the respective lobes 103a, 103b and 103c. Sandwitched between the rotary pole members 102 and 103 is a permanent magnet 105, which is also secured to the distributor shaft 101b by the sleeve member 104. Numeral 106 designates an annular stationary magnetic pole member made of a magnetic material and secured to the inside wall surface of the distributor housing 101a. It has a U-shaped profile in axial section. It is provided along the inner peripheral edges thereof with upper lobes 106a, 106b and 106c and lower lobes 106'a, 106'b and 106'c. The upper lobes 106a, 106b and 106c are flush with the lobes 102a, 102b and 102c of the rotary pole member 102, while the lower lobes 106'a, 106'b and 106'c are flush with the lobes 103a, 103b and 103c of the rotary pole member 103. The upper and lower lobes are located at three of the four positions equally dividing each of the upper and lower inner peripheral edges of the stationary pole member 106. The upper lobes 106a, 106b and 106c axially overlap the respective lower lobes 106'a, 106'b and 106'c. Numeral 107 designates an induction coil accommodated in the annular recess 106d of the stationary pole member 106.

In the operation of the construction described above, with each rotation of the distributor shaft 101b four successive voltage swings are produced in the induction coil 107. When the distributor shaft 101b assumes an instantaneous position as shown in FIGS. 5 to 7, the lobes 102a, 102b and 102c of the rotary pole member 102 and the lobes 103a, 103b and 103c of the rotary pole member 103 respectively come to face the upper lobes 106a, 106b and 106c and lower lobes 106'a, 106'b and 106'c of the stationary pole member 106, thus providing 6 lobe pairs. Around this instant, therefore, the rate of change of the magnetic flux linking with the induction coil 107 becomes extremely large, producing a large voltage swing in the induction coil 107 as indicated at A.sub.1 in FIG. 9a, which shows the induced voltage e versus the angular position .theta. of the engine crankshaft.

After the rotation of the distributor shaft 101b by 90.degree. in the direction of the arrow, the lobes 102a and 106b, 103a and 106'b, 102b and 106'c, and 103b and 106'c come to face each other to provide 4 lobe pairs. Thus, around this instant the rate of change of the magnetic flux is less, producing a small voltage swing in the induction coil 107 as indicated at A.sub.2 in FIG. 9a.

After the rotation of the distributor shaft 101b by further 90.degree., the lobes 102a and 106c, 103a and 106'c, 102c and 106a, and 103c and 106'a come to face each other to provide also 4 lobe pairs. In this manner, the lobes of the rotary pole members 102 and 103 all simultaneously face the corresponding lobes of the stationary pole member 106 only once in each rotation of the distributor shaft 101b, and only four lobe pairs are produced at the other instants of passing-by. Thus, a large voltage swing A.sub.1 and subsequent three small voltage swings A.sub.2, A.sub.3 and A.sub.4 are produced in the induction coil 107 in one rotation of the distributor shaft 101b, as shown in FIG. 9a.

FIG. 8 shows, in block form, a system for converting the waveform of the induced voltage into two different kinds of signals. In the Figure, numeral 110 designates the signal generator according to the invention. The system also includes an integrating circuit 111, a level detector 112, and shaping circuits 113 and 114.

The magnetic flux linking with the induction coil 107 around the angular position .theta., FIG. 9a, is very great compared to that in the vicinity of the other instants of passing-by and is constant irrespective of the engine speed. Thus, by integrating the induced voltage the vicinity of the particular angular position .sub.1 may be discriminated.

As is mentioned earlier time, integrating the induced voltage e

e = k(d.phi./dt),

where k is proportionality constant, and .phi. is the magnetic flux linking with the coil, yields

Hence, the integral is independent of the engine speed.

Accordingly, the voltage output from the signal generator 110 is integrated by the integrating circuit 112, and the portion of the integrated output at a level corresponding to the large voltage swings A.sub.1, FIG. 9a, is discriminated by the level discriminator 112 and shaped by the shaping circuit 113.

FIGS. 9b and 9c show the waveforms of the outputs of the shaping circuits 114 and 113, with the angular position .theta. being common to FIG. 9a. The waveform of FIG. 9c enables detecting the particular angular position .theta..sub.1, which may correspond to, for instance the top dead center of a particular cylinder. On the other hand, the waveform of FIG. 9b, which is provided by the shaping circuit 114 directly shaping the waveform of FIG. 9a, enables detecting, for instance, the top dead center of the individual cylinders.

While some preferred embodiments of the invention have been described in the foregoing, they are by no means limitative. For example, less than three lobes may be provided to the rotary pole members 102 and 103 and the inner peripheral edges of the stationary pole member 106 in the preceding embodiment. Also, one of the rotary pole members 102 and 103 may be dispensed with. In this case, the stationary pole member 6 need not be U-shaped and may have lobes corresponding in number to the number of only the lobes of the remaining rotary pole member. Further, the signal generator according to the invention may be provided, if necessary, outside and separately of the distributor.

Claims

We claim:

1. A signal generating system for use with internal combustion engines comprising:

a generator having a coil and magnetic means which are relatively movable with rotation of an engine, said magnetic means adapted to provide magnetic flux linked with said coil at relative positions between said magnetic means and said coil corresponding to a plurality of predetermined angular positions of the crankshaft of the engine and provide a larger magnitude of said magnetic flux at one of said relative positions corresponding to a specific one of said predetermined angular positions than those at the remaining positions, said coil adapted to induce a voltage at each of said relative positions in accordance with changing rate of the magnitude of said magnetic flux linked thereto;

a first detector connected in circuit to said armature coil for producing a first pluse signal when said voltage induced into said armature coil exceeds a predetermined value; and

a second detector connected in circuit to said armature coil and having an integrator for integrating said voltage induced into said armature thereby producing an integrated voltage signal and means for producing a second pulse signal when said integrated voltage signal exceeds a predetermined value.

2. A signal generating system according to claim 1 wherein said generator comprises:

rotary pole means secured to a shaft rotatable in synchronism with said engine crankshaft, said rotary pole means having a plurality of pole tips;

stationary pole means having a plurality of pole tips; and

a permanent magnet adapted to provide magnetic flux through said rotary pole means, said stationary pole means and said coil thereby inducing said voltage into said coil with rotation of said crankshaft;

a specific one of said pole tips of said rotary pole means adapted to permit a large magnitude of magnetic flux to be passed through said coil when said specific pole tip faces to a specific one of said pole tips of said stationary pole means than when said first-mentioned specific pole tip faces to any one of the remaining pole tips of said stationary pole means.

3. A signal generating system according to claim 2 wherein each of said rotary and stationary pole means are provided with the same number of said pole tips respectively disposed on the periphery thereof with a uniform angular interval, said number being determined from a desired number of pulses produced by said coil each rotation of said rotary pole means, and each of said specific pole tips of said rotary and stationary pole means has a facing area larger than those of the remaining pole tips.

4. A signal generating system according to claim 2 wherein each of said rotary and stationary pole means are provided with said pole tips at positions on the periphery thereof spaced with a uniform angular interval except for one of said positions, the number of said pole tips being determined by a desired number of pulses produced by said coil each rotation of said rotary pole means.